Which properties should I read in a Mesh struct inside the .blend file?
For a basic engine you need to extract mvert which is an array of the vertices of the model. Within an item of this array the co attribute will contain the local vertex coordinate of a vertex. the no attribute contains the normal of that vertex.

The mpoly contains the face data as edge loops around the face. As a face within Blender can contain a finite amount of vertices you will need to triangulate the faces yourself. At forehand in blender, or later in your own code. An mpoly contains a loopstart as an index into mloop and a totloop as number of sequential entries that construct the face.

The mloop contains the data for the edge loops. It has a v for vertex index and a e as edge index.